Radio antenna



March 23, 1937. H. E. SJGSTRAND RADIO ANTENNA Filed Sept. 30, 1933 fiL/ALMAR 25, 510571 34; y H/s Attorneys Patented Mar. 23, 1937 UNITED STATES PATENT OFFICE RADIO ANTENNA Application September 30, 1983, Serial No. 691,700

Claims.

My invention particularly relates to a type of antenna known as a loop antenna which comprises two loops or pluralities of windings of electrical conductors angularly disposed with 5 respect to each other and connected therebetween so that the two loops will operate in conjunction and with the result that the receiving set operated therewith will have an extremely selective characteristic.

In most cities, particularly those having a large population, there are located a great number of radio broadcasting stations some of which are in closely spaced angular relationship with some receiving sets. The operators of such receiving sets would encounter considerable difficulty in separating the radio waves emanating from those broadcasting stations which are so situated with respect to their receiving sets. The loop antenna has been used considerably in large cities to provide a satisfactory and selective means for radio reception. However, an operator of a receiving set situated in the position as described above would still encounter considerable interference when attempting to tune in on one of the stations lying within that limited angular range.

By using two loops connected together to cooperate in conjunction with each other and disposed at a comparatively small angle, the degree of selectivity is greatly increased over that of the single loop and where some broadcasting stations are situated within a comparatively small angular distance from the receiving set one of them may be selected without encountering the annoyance of interference.

My invention, therefore, has for an object the utilization of two loops wound and connected together in the manner hereinafter more specifically pointed out, to provide a high degree of selectivity. A further object of my invention is a loop antenna adaptable as a very sensitive and accurate means for direction finding.

Further objects of my invention will be more particularly pointed out in the following description and appended claims, and will best be understood by reference to the accompanying drawing in which I have illustrated a preferred embodiment thereof and in which- Fig. 1 is a perspective View of the device embodying my invention;

Fig. 2 is a diagrammatic illustration of the device in operative relationship to a given broadcasting station;

Fig. 3 is a View similar to Fig. 2 and illustrating my device in a position unresponsive to a given station; and

Fig. 4 is a view similar to Figs. 2 and 3 illustrating my device in a position at right angles to that shown in Fig. 2.

Like reference characters indicate like parts throughout the drawing.

Referring now to the drawing, [0 indicates a frame having any desired shape, preferably rectangular, and on which is wound a coil ll of electrical conducting material, such as copper wire or the like, which may or may not bear insulating coverings. In the event bare wire is used, the coils are insulated by suitable separators disposed around the outer surface of the frame. A second frame I2 is mounted in angular relationship to frame In and has wound thereon a second wire coil I3. The angle formed by the two frames and conductors mounted thereon may be of any degree though a small angle is preferable for the most satisfactory operation of my device. In the embodiment illustrated in Fig. 1, the frames I0 and I I are integral and the frames together with the conductors mounted thereon, as indicated generally at A and B, respectively, are rotatably mounted on a support which comprises a base I4 and an upstanding shaft IE to which said loops are attached. The shaft I5 may be mounted on base I4 in any suitable manner so that the shaft and the loops supported thereby may be rotated to positions responsive to selected broadcasting stations. An indicator arm I6 is illustrated as fixed with respect to said rotatable loops and may be used in conjunction with a properly calibrated dial on the base 14 so that an operator may more easily locate a station from which he desires to receive electro-magnetic waves.

One end ll of the coil l l is connected to the end 18 of coil I3 as by an electrical conductor 2| and the other end [9 of coil H is connected by a sec-- ond electrical conductor 22 to the end 20 of coil l3. The output taps 23 and 24 of the antenna are disposed between the two coils and connected at points 25 and 26 respectively. In the embodiment illustrated in Fig. 2, I have illustrated a tuning coil 21 included in the antenna circuit, that is between the output taps 23 and 24. Two tuning coils 28 and 29 form an inductive coupling between the antenna coil 2! and the receiving circuit. It is, of course, to be understood that block condensers may be substituted for the coils illustrated or any form of coupling may be interposed between the antenna and the receiving sets as determined by the character of the receiving set.

Assuming in Figs. 2, 3 and 4 that a broadcasting station lies in a direction illustrated by the broken line 30, the lines of force of an active radio magnetic field emanating from said station will lie substantially perpendicular to the line of direction of said station from the antenna and in the drawing the direction of this field is illustrated by the broken line 3i.

It is to be understood that the loops A and B, as illustrated, are intended to represent coils which are wound in the same direction. That is to say, assuming the ends l8 and 19 of the coils l3 and II, respectively, to be the starting points of the loops then it is intended that the coils be wound, for example, in a clockwise direction. The coils are then connected together, as illustrated, in a manner to produce, when placed substantially perpendicular to the magnetic field, opposed electromotive forces at their points of interconnection. From the foregoing it is evident that for all positions of the loops wherein the ends l8 and i9 of the coils lie to the same side of the line 3|, the coils, being wound in the same direction, will have currents induced therein which will flow in the same direction with respect to the electromagnetic field. Hence, by connecting the loops as hereinbefore pointed out, for all positions of said loops, except where the ends l8 and Hi thereof lie on opposite sides of the line 3|, the induced electromotive forces therein will be opposed and hence no antennae currents will flow from the output taps to the receiver. Obviously, if the coils are wound in opposite directions with the ends [8 and E9 of the coils as starting points, the coils would be interconnected in the reversed manner to that illustrated.

In Fig. 2 the loops A and B lie in such a position that the radio magnetic field will induce electromotive forces therein, the electromotive forces in each coil causing an antenna current to flow therefrom, through the output tap 23, as illustrated, and through the coil 2'! to the points I! and l8 at the opposite ends of the coils. The arrows on the drawing indicate the assumed direction of fiow of the antenna current in the loops A and B and the coupling circuit associated therewith. Hence, in Fig. 2 it may readily be seen that the currents in both coils fiow through the output tap 23 through the coil and back through the output tap 2 The direction of flow of antenna current is dependent upon the position the conductors of the antenna assume with respect to a given radio magnetic field. Referring to Fig. 2, it will be seen that loops A and B have assumed such a position that the line (H representing the active radio magnetic field is included by the acute angle between said loops and intersects the loops at their points of intersection. In this position an electromotive force will be induced in loop A causing a current to fiow in the direction indicated by the arrow 32 and in loop B also will be induced an electromotive force causing a current to flow in the direction indicated by the arrow 33. The conductors in loop A lie across the radio magnetic I field so that the electromotive force induced therein causes the current to fiow; we will assume for the purpose of illustration, from left to right in the radio magnetic field as viewed in Fig. 2. Likewise, the current will fiow in loop B in a similar direction that is from left to right in the radio magnetic field. In Fig. 8, the loops have been turned through a small angular distance so that loop A lies in a position substantially at right angles to the line 30, indicating the direction of the broadcasting station, and parallel with the line 3|, which indicates the direction of the active radio magnetic field. In this position the conductors in loop A do not lie across the magnetic field and hence are in a position in which no electromotive force is induced in the loop and consequently no current flows therein. The loop B, in this position, will have induced therein a current fiowing in the same direction as that illustrated in Fig. 2, the conductors in loop 13 lying across the magnetic field in the same way as in Fig. 2. Inasmuch as there is no current fiowing in loop A it will operate as a shunt across loop B and because the two loops are preferably designed to have substantially equal inductances no current will fiow through the output taps 23 and 24 to the coil 27 in the antenna coupling circuit. In Fig. 4 the loops have been turned to a position substantially at right angles to that illustrated in Fig. 2 and in this position it will be seen as designated by the arrows that the electromotive forces induced in the two loops are opposed to each other and consequently no antenna current flows to the coil 21. The conductors in the loops A and B lie across the radio magnetic field in the same way so that assuming that the currents induced therein fiow from left to right in the magnetic field the current in loop B will be fed back through the connector 22 to the loop A and likewise the current in loop A fed back through the connector 2i to loop B. It will be seen, therefore, from the foregoing description that the antenna in the position illustrated in Fig. 2 will have additive electromotive forces induced in the loops A and B with the result that an antenna current flows through the coil 21, whereas, in Fig. 4 the induced electromotive forces are opposed to each other and no current flows from the antenna to the coil 21. Figs. 2, 3 and 4 illustrate by way of example all the possible, difierent operating positions the loop antenna can assume with respect to a given broadcasting station and the only positions thereof in which an antenna current fiows through the antenna coupling circuit are, as diagrammatically illustrated, when the loop antenna is placed in a position wherein the angle between the loops A and B is intersected by the line representing the active radio magnetic field, in other words, when the loops lie across the magnetic field in such a position that the antenna current in each loop fiows toward the same point of connection and output tap.

From the foregoing description it is, of course, obvious that my antenna is in an operative position with respect to a given broadcasting station when the loops lie in a position near the point at which a minimum signal strength is received. This is, of course, necessary due to the arrangement and interconnection between the two loops A and B in order to provide a loop antenna having a high degree of selectivity.

Furthermore, it is to be understood that the term loop in the specification and claims includes any inductive means which may be used such, for example, as a plurality of windings of wire or bands of metal, the essential feature residing in the provision of two inductive coils so arranged and connected together as to permit the reception of radio magnetic waves, for example, from any desired station of several broadcasting stations lying within a comparatively small, angular zone, having the receiving station as an apex.

While I have described my invention in its preferred embodiment, it is to be understood that the words which I have used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of my invention in its broader aspects.

What I claim is:

l. A radio antenna comprising two rotatably mounted loops disposed in fixed, acute angular relationship and output taps; said loops being connected across said output taps to produce additive potential differences thereacross for posi- 10 tions of said loops wherein the acute angle formed therebetween includes a line representing the direction of the lines of force of a radio magnetic field.

2. A radio antenna comprising two rotatably 5 mounted loops disposed in fixed, acute angular relationship and output taps adapted for electrical connection with the input terminals of a receiver; said loops being connected across said taps to submit additive induced currents to said 20 receiver for positions of said loops wherein the acute angle formed therebetween includes a line representing the direction of the lines of force of a radio magnetic field and to submit substantially zero currents thereto for all other positions 25 of said loops.

3. A radio antenna comprising two loops disposed in fixed, acute angular relationship and output taps adapted to be electrically connected to a receiver; said loops being wound and connected in multiple to said taps to produce added, induced currents flowing through said taps to said receiver when the acute angle formed between said loops includes a line representing the direction of the lines of force of a radio-magnetic field.

4. In a radio antenna, two loops disposed at a substantially small angle with respect to each other, said loops being wound and connected together in multiple to produce opposed electromotive forces for all positions of said loops wherein the obtuse angle formed therebetween includes a line representing the direction of the lines of force of a radiomagnetic field.

5. A radio antenna comprising two loops formed of continuous convolutions of electrical conductors disposed in substantially small angular relationship, the ends of said convolutions being connected together to form a closed circuit whereby opposed electromotive forces are induced in said loops for all positions thereof wherein the obtuse angle formed therebetween includes a line representing the direction of the lines of force of a radiomagnetic field.

HJAIMAR E. SJ GSTRAND. 

